Process for producing methanol-formaldehyde solution of low-water content

ABSTRACT

A gaseous stream from a formaldehyde converter is introduced into a concentrator-absorber wherein the gaseous stream is scrubbed countercurrently with an aqueous formaldehyde solution from a water absorber of a conventional formaldehyde plant. The bottom stream withdrawn from the concentrator-absorber is recirculated to the top of the concentrator-abosrber and a portion of this stream is withdrawn and mixed with methanol to provide a methanol-formaldehyde solution of the desired concentration.

ilnite States Patent [72] Inventor Charles William DeMuth Unadilla, N.Y.

[21] Appl. No. 35,847

[22] Filed May 8, 1970 [45] Patented Dec. 28, 1971 [73] Assignee BordenInc.

New York, N.Y.

[54] PROCESS FOR PRODUCING METHANOL- FORMALDEHYDE SOLUTION OF LOW-WATERCONTENT 14 Claims, 1 Drawing Fig.

[52] US. Cl 55/89,

[51] Int. Cl B01d 47/00 [50] Field of Search 55/25,27,

[56] References Cited UNITED STATES PATENTS 2,527,655 10/1950 Pyle eta1. 203/17 2,676,143 4/1954 Lee et a1. 203/17 3,214,891 11/1965 Kloepperet a1. 55/56 3,243,939 4/1966 De Rooij 55/39 3,289,391 12/1966 De Rooijet a1. 55/89 3,493,472 2/1970 Schumacher 203/17 X Primary ExaminerReuben Friedman Assistant ExaminerR. W. Burks Allomeys-George P. Maskas,Edward L. Mandel] and George A. Kap

l VENT GAS 11 A1 R 62 J 3 t 5 4 f METHANOL STORAGE a E a: gen 1 3 10.1:g M 8m: CC 3 LUU 50 a. n: m L o 6 EXISTING FORMALDEHYDE 16 PLANTMETHANOL g FORMALDEHYDE l- 24 PLANT g5 8 Pa; 1 in: g8 18 2 02 7/ U MlXTANK 32 36 TO STORAGE PATENTED UEC28I97I, 3329397 F VENT GAS A! R 62 A3\ t 5 r4 METHANOL STORAGE k Em 65 r E 3 L 2% CT: 3 8U 60 (L 0: m

U an EXISTING v FORMALDEHYDE PLANT METHANOL c: FORMALDEHYDE g 24 PLANTE5 CD in: g8 26 o I 52 3s JVL l CHARLES WILLIAM DE MUTH INVENTOR.

Q KL *mim w TO STORAGE PROCESS FOR PRODUCING METHANOL- FORMALDEHYDESOLUTION OF LOW-WATER CONTENT This invention relates to a process forproducing methanolformaldehyde solution of a low water content.

Alkanol-formaldehyde solutions have become important in the productionof specialty resins, particularly for use in protective coatings and intextile applications. Since it is important, in many instances, thatsuch solutions have low water content, they are now ordinarily producedby dissolving paraformaldehyde product of specified composition. Thismethod requires, first, the production of paraformaldehyde, and then,the additional step of dissolving such material in an alkanol. Inanother method, an aqueous formaldehyde solution, enriched with respectto formaldehyde, is prepared and then mixed with an alkanol to obtain aproduct of desired composition.

Kloepper et al. US. Pat. No. 3,214,891 describes a process for preparingalkanol-formaldehyde solutions by partially condensing a gaseousformaldehyde stream to produce a waterenriched condensate and aformaldehyde-enriched vapor; separating the condensate and the vapor;and introducing the vapor into an alkanol absorber to absorbsubstantially all of the formaldehyde in the alkanol. This process iscumbersome in that it requires more process steps and additional equipment.

It is an object of this invention to provide a process for producingmethanol-formaldehyde solutions of a low water content without requiringthe production of highly concentrated formaldehyde or paraforrnaldehyde.

Another object of this invention is a process for producingmethanol-formaldehyde solutions of low water content by absorbing theproduct vapors, emanating from the formaldehyde converter, in an aqueoussolution, concentrating this solution with respect to formaldehyde andadding a predetermined amount of methanol to obtain a solution ofdesired compositron.

Another object is a process for producing methanol-formaldehydesolutions of low water content without resorting to evaporation ordistillation procedures.

Briefly stated, the present invention pertains to a process forproducing methanol-formaldehyde solutions of low water content. Thisprocess is characterized by the fact that gaseous effluent from theformaldehyde converter is passed through a concentrator-absorber andthen blended with methanol to adjust the composition of themethanol-formaldehyde solution to the desired specification.

Gaseous effluent is obtained from conventional formaldehyde plantswherein formaldehyde is produced either by the methanol or thehydrocarbon processes. In the methanol process, a mixture of methanolvapor and air is passed over a stationary catalyst at approximatelyatmospheric pressure and the product gases are absorbed in water.Methanol is vaporized by either flash vaporization, which is then mixedwith air under controlled conditions, or by passing air through methanolmaintained at a temperature required to obtain the desired mixture.Precautions are taken to avoid explosive mixtures of methanol and air.The feed vapors, usually preheated, are passed into the converters orburners which may consist of jacketed vessels containing a shallow bedof catalyst such as silver, or copper, or iron-molyhdenum oxide. Gaseouseffluent is passed directly to a scrubber where the gases are cooled andthe formaldehyde is absorbed by countercurrently circulating solution.The ofi' gases, or inerts, are taken off the top of the scrubber. Theproduct solution, which contains some methanol, must be adjusted to meetcustomer requirements with respect to its methanol and formaldehydecontents. Excess methanol may be removed by fractionation so that asubstantially methanol-free solution can be obtained, if desired.

In the silver-or-copper catalyzed methanol process, the methanol-airvapor mixtures contain up to 50 percent by volume of methanol and thetemperature in the reactor may vary between 450 and 650 C., withan'optimum temperature being at about 635C. The off gases contain 18-20percent hydrogen and less than l percent oxygen. Conversions in therange of 60-73 percent have been attained, with net yields of 83-92percent. The product solution contains unreacted methanol.

The methanol-air mixtures used in the oxide-catalyst process containonly 540 percent methanol. Reaction temperatures are 300-430 C. and theyields are somewhat higher than those for the silver-catalized process.

The hydrocarbon process involves partial oxidation of a hydrocarbon gaswith air or oxygen under pressure, followed by rapid cooling,condensation, and absorption of the products in water to give a crudesolution which must then be refined to separate formaldehyde from theother reaction products such as methanol, acetaldehyde, propyl alcohol,propionaldehyde, and organic acids. Formaldehyde is isolated as a dilutesolution, which must be concentrated to market strength. This solutionis not the major product from these processes, the quantity anddistribution of other products being dependent on the hydrocarbon rawmaterial and processing technique.

The invention disclosed herein is illustrated by the attached flowdiagram wherein the feed stream consists of an effluent stream leavingthe converter in which the methanol-air mixture is converted to productvapors. The flow diagram illustrates the methanol-formaldehyde plant inconjunction with an aqueous-formaldehyde plant. Amount of the gaseouseffluent or product vapors from the converter diverted to thealcohol-formaldehyde plant will depend on the relative requirements ofthe corresponding product solutions and other factors.

Referring to the attached flow diagram, the gaseous effluent streamleaving converter 10 is divided into two parts: one part is delivered tothe water absorber 62 in the conventional aqueous formaldehyde plant,and the other part is introduced into the concentrator-absorber 14 ofthe alcohol formaldehyde facility. The gaseous effluent stream fromconverter 10, which uses silver catalyst and rich methanol-air mixtures,generally includes l035 percent formaldehyde, 520 percent methanol, 5-25percent water and 40-75 percent inerts consisting mostly of nitrogen,oxygen, carbon dioxide, carbon monoxide, hydrogen and methane. Theportion of the gaseous effluent designated as inerts constitute thosegases which are not absorbed in the concentrator-absorber 14. In theproduction of many preferred solutions, a water content of less thanabout 10 percent in the gaseous effluent is desired.

The gaseous effluent is delivered to the concentrator-absorber by way ofline 12 at a temperature of about to 450 C., and preferably at atemperature of to 200 C. The pressure in line 12 may vary from l0p.s.i.a., to 20 p.s.i.a., but is preferably atmospheric.

In the conventional aqueous formaldehyde plant illustrated in the flowdiagram, the gaseous effluent stream introduced into water absorber 62by means of line 60 is passed countercurrently to a weakaqueous-formaldehyde solution which is introduced into water absorber 62from secondary water absorber 3 through line 4. Water is introduced intothe secondary water absorber 3 through line 5 and a weakaqueous-formaldehyde solution from absorber 62 is likewise recirculatedto the upper portion of said absorber by way of line 64.

Any one of the several commercial types of absorbers, such as sieve traycolumns, bubble cap columns and vapor-liquid contactors, in general, maybe used which are effective in promoting absorption of the vapors in thecirculating solution.

The gaseous effluent stream introduced into concentratorabsorber 14 isscrubbed with the concentrated formaldehyde recirculating solution inline 18 and aqueous-formaldehyde solution from water absorber 62introduced into concentrator-absorber 14 by way of line 66. Theoperating pressure and temperature at the top of concentrator-absorber14 will vary from 10 p.s.i.a. to 20 p.s.i.a. and from 75 to C.; andpreferably from 13 p.s.i.a. to 17 p.s.i.a. and 75 to 90 C. At the bottomof the concentrator-absorber 14, the pressure will vary between 1 l and21 p.s.i.a. while the temperature will be in the range of 85-125 C.Recirculating solution 18 consists essentially of 60 to 75 percentformaldehyde, 15 to 25 percent methanol and 5 to percent water. Thepreferred composition of the recirculating solution 18 is as follows:71-73 percent formaldehyde, 17-19 percent methanol and 7-12 percentwater. The temperature of recirculating stream must be maintained aboveabout 85 C. since temperatures below about 80 C. are detrimental to theprocess because methanol would be flashed-off before water, as one wouldnormally expect. At temperatures above about 85 C., water is vaporizedfrom the recirculating solution before methanol although methanol boilsat 65 C. while water, at 100 C.

The portion of the aqueous-formaldehyde recirculating solution 64diverted from water absorber 62 to concentratorabsorber 14 through line66 may be introduced into concentrator-absorber 14 either at the upperportion thereof or mixed with recirculating stream 18 and thenintroduced into the concentrator-absorber. The temperature of theaqueous formaldehyde stream 64 is in the range of 40 to 125 C. and itscomposition consists essentially of 30 to 50 percent formaldehyde, 15 to30 percent methanol and to 35 percent water. The composition of atypical aqueous-formaldehyde stream 64 is 46 percent formaldehyde, 23percent methanol and 31 percent water.

The aqueous-formaldehyde recirculating stream 66 is introduced into theconcentrator-absorber 14 to provide a scrubbing liquid for the gaseouseffluent entering the concentrator absorber through line 12. Proportionof the aqueousformaldehyde recirculating solution that is introducedinto the concentrator-absorber to the concentrated formaldehyderecirculating solution 18 entering the concentrator-absorber is in therange of 1:20 to 1:100, and preferably in the range of 1:30 to 1:50, onweight basis. Concentrator-absorber receives the aqueous-formaldehydesolution from water absorber 62 and allows it to come in contact withthe gaseous effluent from converter 10 thus concentrating theaqueous-formaldehyde solution with respect to its formaldehyde content.

A portion of the aqueous formaldehyde solution may be withdrawn fromline 64 through line 65.

The unabsorbed vapors in concentrator-absorber 14, consistingessentially of inerts and a small amount of water, formaldehyde andmethanol, are passed through line 16 into line 60 where they are mixedwith the gaseous effluent from converter l0 and introduced into waterabsorber 62. The unabsorbed vapors leave concentrator-absorber at atemperature of 70 to 125 C. and a pressure of 10 p.s.i.a. to 20p.s.i.a., and preferably at 85 to 95 C. and 13 to 17 p.s.i.a. A typicalcomposition of the unabsorbed condensibles in the vapor stream is asfollows:

CH O 32.5% CH OH40.0% H O 27.5%

A portion of the recirculating solution 18 is withdrawn through line 24and pumped into mix tank 26. The proportion of the recirculatingsolution returned to the concentrator-absorber to the recirculatingsolution withdrawn from the recirculating circuit is in the range of :1to 50:1. Methanol is added to the mix tank in a predetermined amountthrough line 28. Methanol and the solution delivered through line 24 aremixed by circulating the mixture through pump 30 by way of lines 32, 34.A side stream 36 is withdrawn from mix tank 26 or from line 34 andstored as the final methanol-formaldehyde solution product.

In an embodiment which is not illustrated in the drawing, the necessityof the mix tank 26 can be dispensed with by blending methanol line 28with the concentrated formaldehyde solution from line 24 and introducingboth directly into line 36.

EXAMPLE formaldehyde water methanol inerts such as nitrogen. hydrogen,carbon dioxide,

etc.

The pressure at the exit of the converter was substantially atmosphericand the temperature of the gaseous effluent was 125C. Of the totalgaseous effluent produced in the converter, 1,205 c.f.m., measured atSTP, were introduced into the water absorber and 395 c.f.m. wereintroduced into the concentrator-absorber. The vapors introduced intoconcentrator-absorber were scrubbed with aqueous formaldehyde solutionfrom the water absorbed, which was introduced into the upper portion ofconcentrator-absorber through line 66 at the rate of 1 g.p.m., andrecirculating solution 18. The aque ous formaldehyde solution was at thetemperature of 60C. and had the following composition:

47% formaldehyde 23% methanol 30% water The temperature and pressure atthe top of the concentratorabsorber was C. and 15 p.s.i.a., while at thebottom thereof, it was C. and 16.0 p.s.i.a. The unabsorbed vapors fromthe concentrator-absorber were passed through line 16 and into line 60at a rate of 375 c.f.m. These vapors were at substantially atmosphericpressure and at a temperature of 78 C. The composition of the vapors wasas follows:

19.0% CH 0 23.3% CH;,Ol-l 16.2% H 0 41.5% Inert A stream of concentratedformaldehyde solution was withdrawn from the concentrator-absorber at arate of 50 g.p.m. This stream was at a temperature of 85 C. and had thefollowing composition:

72% formaldehyde 17% methanol 1 1% water One g.p.m. of this stream waswithdrawn from line 18 and introduced into mix tank where it was mixedwith a sufficient amount of methanol to provide a methanol-formaldehydeof the following composition:

55% formaldehyde 34% methanol 1 l% water The main objective of theprocess described above is to remove water from the aqueous formaldehydesolution introduced into the concentrator-absorber and thus concentratethe solution with respect to formaldehyde. This objective is achieved bymaintaining the temperature of the liquid at the bottom of theconcentrator-absorber preferably below C. to drive off water. Althoughwater is driven off, most of the methanol remains in solution. Thisoutcome is unexpected in view of the respective boiling points ofmethanol and water, i.e., 65 v. 100 C.

There are two principal advantages of the herein-described process overanalogous prior art processes:

1. economics, and 2. absence of paraformaldehyde formation. My processis more economical than the known processes for producingmethanol-formaldehyde solutions because it is simpler and requires lessequipment. in the past, methanol-formaldehyde solutions were prepared bydistilling primary solutions containing formaldehyde, methanol and waterto obtain concentrated formaldehyde solutions of about 85 percentformaldehyde and 15 percent water which concentrated solutions were thenblended with enough methanol to result in the desiredmethanol-formaldehyde composition. Since the boiling point of methanolis 65 C. and since the water content of 5 the primary solutions was toohigh, distillation was resorted to remove excess water. In the processof distilling the water off, methanol was completely removed because itsboiling point is lower than that for water. The hereindescribed processavoids the necessity for a still and avoids the distillation procedures.In accordance with my process, a methanol-forrnaldehyde solution isprepared by scrubbing a portion of the gaseous effluent from afonnaldehyde converter with an aqueous formaldehyde solution obtainedfrom a conventional formaldehyde plant to obtain a concentrated aqueousformaldehyde solution which is subsequently blended with a predeterminedamount of methanol.

Formation of the paraformaldehyde precipitate is avoided in the case ofmy formaldehyde solutions since they are stable at temperatures down toabout 70 C. This is not the case with the concentrated formaldehydesolutions of the past. Solutions prepared by conventional procedures arenot stable below 100 C. and will polymerize if maintained even about 100C. for an extended duration. The fact that my solutions are stable atlower temperatures also has the inherent benefit of inhibiting formationof fomiic acid.

Iclaim:

1. In a process for producing aqueous formaldehyde solution comprisingpassing a gaseous efiluent from a formaldehyde converter using a silvercatalyst, to a water absorber;

introducing an aqueous solution into the water absorber countercurrentlyto said gaseous effluent for the purpose of scrubbing said gaseouseffluent of its water-soluble constituents;

withdrawing a liquid stream from the lower portion of the waterabsorber;

recirculating at least a portion of said liquid stream to the upperportion of the water absorber; the improvement being a process forproducing a methanol-formaldehyde solution which comprises introducing aportion of said gaseous effluent into a concentrator-absorber;

introducing a portion of said liquid stream into theconcentrator-absorber wherein said gaseous effluent is scrubbed withsaid liquid stream;

withdrawing a concentrated formaldehyde solution from the lower portionof the concentrator-absorber;

recirculating at least a portion of said concentrated formaldehydesolution to the upper portion of the concentrator-absorber;

withdrawing a portion of said concentrated formaldehyde solution; and

mixing the portion of said concentrated formaldehyde solution withsufficient amount of methanol to obtain a methanol-formaldehyde solutionof the desired composition.

2. Process of claim 1 wherein the temperature and pressure at the top ofthe concentrator-absorber is 75 to 125 C. and to 20 p.s.i.a.,respectively, while at the bottom, the respective values are 85to 125C.and 11 to 21 p.s.i.a.

3. Process of claim 2 wherein the composition of said gaseous efiluentis 10-35 percent formaldehyde, 5-20 percent methanol, 5-25 percent waterand 40-75 percent inerts, the temperature of said gaseous effluent atthe exit of the forrnaldehyde converter is in the range of 450 to 650 C.

4. Process of claim 3 wherein pressure of said gaseous effluent at theexit of the formaldehyde converter is 10-20 p.s.i.a.

5. Process of claim 1 wherein proportion of said liquid stream from thewater absorber introduced into the concentrator-absorber to theconcentrated formaldehyde solution recirculated to theconcentrator-absorber is in the range of 1:20 to 1:100.

6. Process of claim 1 wherein said mixing of methanol with saidconcentrated formaldehyde solution is carried out in-line.

7. Process of claim 1 including the steps of venting unabsorbed vaporsfrom the water absorber;

withdrawing unabsorbed vapors from the concentrator-ab sorber; and

introducing unabsorbed vapors from the concentrator-absorber into thelower portion of the water absorber.

8. Process of claim 7 including the steps of combining the gaseouseffluent going to the water absorber with the unabsorbed vapors from theconcentrator-absorber; and introducing this mixture into the waterabsorber. 9. Process for producing methanol formaldehyde solutioncomprising introducing gaseous effluent from a silvercatalyst-fon'naldehyde converter to a concentrator-absorber;

introducing an aqueous formaldehyde solution into the concentratorwherein said gaseous effluent is scrubbed with said aqueous fonnaldehydesolution;

withdrawing unabsorbed vapors from the concentrator-absorber;

withdrawing a concentrated formaldehyde solution from theconcentrator-absorber;

recirculating said concentrated formaldehyde solution to theconcentrator-absorber;

withdrawing a portion of said concentrated formaldehyde solution; and

mixing methanol with the portion of said concentrated formaldehydesolution to obtain a methanol-forrnaldehyde solution of the desiredcomposition.

10. Process of claim 9 wherein the temperature and pres sure at the topof the concentrator-absorber is 75 to 125 C. and 10 to 20 p.s.i.a.respectively, while at the bottom, the respective values are to C. and l1 to 21 p.s.i.a.

11. Process of claim 10 wherein the composition of said gaseous effluentis 10-35 percent formaldehyde, 5-20 percent methanol, 5-25 percent waterand 40-75 percent inerts; the temperature of said gaseous effluent atthe exit of the forrnaldehyde converter is in the range of 450 to 650 C.

12. Process of claim 11 wherein proportion of said aqueous formaldehydesolution to said concentrated formaldehyde solution to said concentratedformaldehyde solution that is recirculated into theconcentrator-absorber is in the range of from 1:30 to 1:50, and whereinthe proportion of said concentrated formaldehyde solution that isreturned to the concentrator-absorber to the portion of saidconcentrated forrnaldehyde solution withdrawn from said recirculatingsolution is in the range of from 30:1 to 50:1, the proportions being onweight basis.

13. In the process of claim [2, wherein the temperature of said aqueousformaldehyde solution is in the range of 40 to 125 C. and thetemperature of said concentrated fonnaldehyde solution at the exit fromthe concentrator-absorber is from 85 to 125 C., the process furtherincluding the step of withdrawing the unabsorbed vapors from theconcentrator-absorber.

14. Process of claim 13 wherein composition of said concentratedformaldehyde solution is as follows:

60-75% C11 0 15-25% CH OH 5-l6% H O

2. Process of claim 1 wherein the temperature and pressure at the top ofthe concentrator-absorber is 75* to 125* C. and 10 to 20 p.s.i.a.,respectively, while at the bottom, the respective values are 85* to 125*C. and 11 to 21 p.s.i.a.
 3. Process of claim 2 wherein the compositionof said gaseous effluent is 10-35 percent formaldehyde, 5-20 percentmethanol, 5-25 percent water and 40-75 percent inerts, the temperatureof said gaseous effluent at the exit of the formaldehyde converter is inthe range of 450* to 650* C.
 4. Process of claim 3 wherein pressure ofsaid gaseous effluent at the exit of the formaldehyde converter is 10-20p.s.i.a.
 5. Process of claim 1 wherein proportion of said liquid streamfrom the water absorber introduced into the concentrator-absorber to theconcentrated formaldehyde solution recirculated to theconcentrator-absorber is in the range of 1:20 to 1:100.
 6. Process ofclaim 1 wherein said mixing of methanol with said concentratedformaldehyde solution is carried out in-line.
 7. Process of claim 1including the steps of venting unabsorbed vapors from the waterabsorber; withdrawing unabsorbed vapors from the concentrator-absorber;and introducing unabsorbed vapors from the concentrator-absorber intothe lower portion of the water absorber.
 8. Process of claim 7 includingthe steps of combining the gaseous effluent going to the water absorberwith the unabsorbed vapors from the concentrator-absorber; andintroducing this mixture into the water absorber.
 9. Process forproducing methanol formaldehyde solution comprising introducing gaseouseffluent from a silver catalyst-formaldehyde converter to aconcentrator-absorber; introducing an aqueous formaldehyde solution intothe concentrator wherein said gaseous effluent is scrubbed with saidaqueous formaldehyde solution; withdrawing unabsorbed vapors from theconcentrator-absorber; withdrawing a concentrated formaldehyde solutionfrom the concentrator-absorber; recirculating said concentratedformaldehyde solution to the concentrator-absorber; withdrawing aportion of said concentrated formaldehyde solution; and mixing methanolwith the portion of said concentrated formaldehyde solution to obtain amethanol-formaldehyde solution of the desired composition.
 10. Processof claim 9 wherein the temperature and pressure at the top of theconcentrator-absorber is 75* to 125* C. and 10 to 20 p.s.i.a.respectively, while at the bottom, the respective values are 85* to 125*C. and 11 to 21 p.s.i.a.
 11. Process of claim 10 wherein the compositionof said gaseous effluent is 10-35 percent formaldehyde, 5-20 percentmethanol, 5-25 percent water and 40-75 percent inerts; the temperatureof said gaseous effluent at the exit of the formaldehyde converter is inthe range of 450* to 650* C.
 12. Process of claim 11 wherein proportionof said aqueous formaldehyde solution to said concentrated formaldehydesolution to said concentrated formaldehyde solution that is recirculatedinto the concentrator-absorber is in the range of from 1:30 to 1: 50,and wherein the proportion of said concentrated formaldehyde solutionthat is returned to the concentrator-absorber to the portion of saidconcentrated formaldehyde solution withdrawn from said recirculatingsolution is in the range of from 30:1 to 50:1, the proportions being onweIght basis.
 13. In the process of claim 12, wherein the temperature ofsaid aqueous formaldehyde solution is in the range of 40* to 125* C. andthe temperature of said concentrated formaldehyde solution at the exitfrom the concentrator-absorber is from 85* to 125* C., the processfurther including the step of withdrawing the unabsorbed vapors from theconcentrator-absorber.
 14. Process of claim 13 wherein composition ofsaid concentrated formaldehyde solution is as follows: 60-75% CH2O15-25%CH3OH 5-16% H2O